A persistent problem inhibiting both the development of implantable neural prosthesis for the neurologically handicapped and robust circulatory system hardware involves the passivation and non-hermetic protection of metallic implants. These devices include stimulating electrodes, signal processing integrated circuits, cardiac pacemakers, and drug delivery systems. To address this problem, thin, conformal, biocompatible coatings are required which passivate a variety of substrate surface and have lifetimes measured in years. Although polymeric materials such as Teflon, Silastic, and the Parylenes have excellent chemical and biochemical properties, poor adhesion of the organic coating to the device surface has been the Achilles' heel in virtually every application. During Phase I we demonstrated the feasibility of mechanically interlocking a Parylene topcoat to an electropolymerized primer coating. Our primer is an electrochemically conducting organic polymer. This feature allowed us to electrochemically generate a morphologically rough surface which facilitated the formation of an interlocked composite coating. Post Phase I work with non-conducting electropolymerized organic polymers indicated that these coatings could be intimately interlocked with the conducting primer coat thereby yielding a highly insulating, adherent composite film. In Phase II we will investigate the interfacial nature of the metal/primer/topcoat composite by a variety of electroanalytical and spectroscopic techniques. Means of improving the metal/primer interface and primer/topcoat interface will be explored. Finally, we will coat implantable cardiac hardware supplied to us by a vendor for subsequent evaluation by them.